Multiple Variations, Combined stock.

[crybunni]

So everything I sell is made-to-order clothing and such. Im switching to Shopify from Etsy and I'm not sure why Shopify doesn't seem to have this option.

So say Im selling a made-to-order tanktop, and I only have enough fabric to make 5 tops, but it doesn't matter what size the customer chooses. It doesn't matter if I sell all 5 tops in size small, or if all 5 sales are in different sizes each. However, I can only sell 5 tops TOTAL. The issue with shopify variations is that if i just put each variation as "1 in stock", then I can only sell one top in each size which I don't want. 

So how can I have multiple variations, but one combined stock for the item? Im looking for a free solution if possible, at leat for the time being.